Circuit arrangement with several sensor elements in matrix circuit design

ABSTRACT

The invention relates to i sensor elements that are interconnected in a (n×m) matrix design with nrow conductors and m column conductors, with i,n and m being natural numbers unequal zero and with 1≦i≦n*m. A first conductor end of the n row conductors and m column conductors is connected to an evaluation circuit and every i sensor element is interconnected between two conductors each of the row conductors and the column conductors. The inventive circuit arrangement further comprises at least one return conductor whose first conductor end is connected to the evaluation circuit and whose second conductor end is contacted with the second conductor end of one of the row or column conductors.

[0001] The present invention relates to a circuit arrangement having aplurality of sensor elements in a matrix configuration.

[0002] To interrogate, i.e. to read, passive sensor elements, anelectrical test voltage is generally applied to the sensor element andthe current flowing as a result of the applied voltage is measured. Thisallows the present electrical state of the sensor element to becalculated and permits the variable which is to be measured (pressure,temperature, etc.) to be ascertained. It should be noted that thepassive sensor elements can have a variable resistance, for example,such as pressure-dependent or temperature-dependent resistances, or avariable capacitance. In this context it is clear that the test voltagecomprises a DC voltage or an AC voltage, depending on the sensorelement's property which is to be measured.

[0003] A sensor device having pressure-sensitive sensors can be used, byway of example, in a seat-occupation recognition system for controllingan active passenger hold-back system in a vehicle. Such a sensor matcomprises a plurality of individual pressure-sensitive sensors which areincorporated over the area of the passenger seat, distributed in theseat. The sensors are connected to an evaluation unit which checks thetrigger state of the individual sensors. If the seat is being occupiedby a person, a plurality of the sensors are triggered on account of thenatural weight exerted on the seat by a person, a fact which isrecognized by the connected evaluation circuit as being a state ofoccupation of the seat, and which is forwarded to the airbag controller.

[0004] To be able to interrogate the sensors selectively, each of thesensors needs to be connected to the evaluation circuit in principle. Toreduce the number of connecting lines for this, it is advantageous tooperate the individual sensors in a matrix configuration. This meansthat, with a number of n*m sensor elements, essentially n row conductorsand m column conductors are provided, with one of the sensor elementsbeing connected between a row conductor and a column conductor,respectively. It should be noted in this context that such a matrixconfiguration represents a circuit arrangement. That is to say that amatrix configuration in a real arrangement requires neither the sensorelements to be arranged in a regular grid distribution nor theindividual connecting conductors to run rectilinearly and parallel or atright angles to one another.

[0005] To evaluate a sensor arrangement in a matrix configuration, theprocedure is as follows: first, the entire matrix configuration with theexception of a first column conductor is connected to the samepotential, e.g. to ground. A test voltage is now applied to the firstcolumn conductor and then the current flowing away on the individual rowconductors is measured selectively. This allows the resistance values ofthe sensor elements connected between the first column conductor and thevarious row conductors to be ascertained selectively. If this procedureis repeated for each of the column conductors, all the sensor elementscan be selectively tested in succession. It should be noted at thispoint that it is alternatively possible to apply the test voltage to theindividual row conductors and to measure the current flowing away viathe sensor elements on the column conductors in order to interrogate theindividual sensor elements.

[0006] If such a circuit arrangement having sensor elements is used insafety-related areas, such as in the airbag controller described abovein a vehicle, it is essential to be able to recognize and, ifappropriate, compensate for any malfunction in the circuit arrangementon account of a fault in the conductor. In a simple matrixconfiguration, the result of a conductor break is, by way of example,that all the sensor elements downstream of the conductor break (seenfrom the evaluation circuit) can no longer be read. If the conductorbreak is not recognized by the evaluation circuit, then such a faultresults in the conclusion that the sensor elements in question have notbeen triggered and therefore the actual seat-occupation situation isinterpreted incorrectly. Suitable means therefore need to be providedwhich at least allow the occurrence of a fault to be recognized.

[0007] For this purpose, EP-A-0 895 091 proposes a circuit arrangementin which, besides the n row conductors and the m column conductors, anadditional row conductor and an additional column conductor arerespectively provided. In this case, the free ends of the m columnconductors are connected to the additional row conductor via arespective monitoring resistor, and the free ends of the n rowconductors are connected to the additional column conductor via arespective monitoring resistor. Following the selective reading of then*m sensor elements, the monitoring resistors between the individualcolumn conductors and the additional row conductor and between theindividual row conductors and the additional column conductor are read.If it is not possible to read one of the monitoring resistors, the testsystem can conclude that a conductor has broken in the row conductor orcolumn conductor leading to the monitoring resistor. The appropriate rowor column can then be deactivated by the evaluation circuit, so thatincorrect interpretation of the seat-occupation situation is prevented.

[0008] A drawback of this apparatus is that, when a conductor break isrecognized, the entire column or row affected by this conductor has tobe deactivated and is therefore no longer available for actual situationrecognition. This impairs the resolution of the sensor device, however.

OBJECT OF THE INVENTION

[0009] It is therefore an object of the present invention to propose acircuit arrangement of the generic type which can be used to compensatefor a fault in an interconnect as far as possible.

GENERAL DESCRIPTION OF THE INVENTION

[0010] The invention achieves this object by means of a circuitarrangement having i sensor elements which are interconnected in an(n×m) matrix circuit configuration having n row conductors and m columnconductors, where i, n and m are natural numbers different than zero andwhere 1≦i≦n*m, where a first conductor end of the n row conductors and mcolumn conductors can be connected to an evaluation circuit and whereeach of the i sensor elements is connected between two respectiveconductors from the row conductors and column conductors. In line withthe invention, the arrangement also comprises at least one returnconductor whose first conductor end can be connected to the evaluationcircuit and whose second conductor end is in contact with the secondconductor end of one of the row or column conductors. In the case of theinventive circuit arrangement, at least one of the row or columnconductors is accordingly returned to the evaluation circuit which is tobe connected. If the returned row or column conductor suffers a linebreak, the sensor elements which are in contact upstream of the break inthe line can be read by the actual row or column conductor, while thesensor elements which are in contact downstream of the break (seen fromthe evaluation circuit) can be read via the return conductor. In thisway, all the sensor elements connected to the respective conductor cancontinue to be addressed after a line break and are thus still availablefor the actual determination of the situation.

[0011] It should be noted that, in one advantageous embodiment of thecircuit arrangement, all of the row and column conductors which arepresent can be returned to the evaluation circuit by means of associatedreturn lines. Depending on the use of the circuit arrangement, however,it can be necessary to return just single row or column conductors orelse single groups of these conductors. It should also be noted that theinvention relates both to circuit arrangements in which all the sensorelements are connected between a row conductor and a column conductor,respectively, and to circuit arrangements in which some of the sensorelements are connected between two column conductors or between two rowelements, respectively. Such an arrangement is described in LU-A-90 437,for example.

[0012] In one variant of the invention, the first conductor end of thereturn conductor and the first conductor end of the contacted row orcolumn conductor can be actuated in parallel by the evaluation circuit.In the case of this embodiment, reading can take place downstream of allof the sensor elements connected to the respective row or columnconductor without any conductor break being detected. The simultaneousactuation of the return conductor and of the associated row or columnconductor can be achieved by making contact with the first conductorends of the two conductors, for example. In this case, the number ofconnections in the circuit arrangement is not increased by introducingthe return conductors.

[0013] In one alternative embodiment, the first conductor end of thereturn conductor and the first conductor end of the contacted row orcolumn conductor can be actuated separately by the evaluation circuit,i.e. each of the first conductor ends of the row or column conductor andof the return conductor can be connected to the actuation apparatusseparately. In such a embodiment, the return conductor can be actuated,by way of example, only if one of the sensor elements connected to thereturned row or column conductor is not producing a signal during theactual interrogation. If the sensor element in question is theninterrogated via the return conductor and if the evaluation circuitreceives a signal corresponding to a switching state in this context,clear inference of the existence of an interconnect break is possible.This state can be stored in an error store by the evaluation circuit,for example, and, in the case of a seat-occupation sensor for a vehicle,can be indicated to the driver by means of a warning light ifappropriate. If no signal is measured when the sensor element inquestion is interrogated via the return conductor, then the alternativesare that the sensor element has not been triggered, is faulty or thatboth lines reveal a line break. In this case, it is accordingly notpossible to make a clear statement about the state of the circuitarrangement.

[0014] In one particularly advantageous embodiment of the invention, thecircuit arrangement therefore has an additional row conductor, with thesecond conductor end of at least one column conductor, preferably of allthe column conductors, being in contact with the additional rowconductor. In this case, the contact can be made by means of a resistorelement, for example. This embodiment allows both the returned columnconductor and the associated return conductor to be checked by checkingthe respective resistance for the additional row conductor. This allowsclear establishment of whether and, if appropriate, in which conductor aline break has occurred.

[0015] In order to ensure the monitoring function of the arrangement inthe event of a line break in the additional row conductor, thearrangement preferably has a return conductor whose first conductor endcan be connected to the evaluation circuit and whose second conductorend is in contact with the second conductor end of the additional rowconductor.

[0016] In a similar manner to the additional row conductor, the circuitarrangement can also have an additional column conductor, with thesecond conductor end of at least one row conductor being in contact withthe additional column conductor. In this case too, the contact is madeby means of a resistor element, for example, and there is advantageouslya return conductor whose first conductor end can be connected to theevaluation circuit and whose second conductor end is in contact with thesecond conductor end of the additional column conductor.

DESCRIPTION WITH REFERENCE TO THE FIGURES

[0017] The text below describes an embodiment of the invention withreference to the appended figures, in which:

[0018] FIG.: 1: shows a first embodiment of a circuit arrangement inaccordance with the invention, with every row conductor and every columnconductor returned,

[0019] FIG.: 2: shows an embodiment of the invention with monitoringresistors.

[0020] A first embodiment of the inventive circuit arrangement is shownin FIG. 1. The circuit arrangement comprises a multiplicity of rowconductors R1, R2, . . . , Rn and a multiplicity of column conductorsC1, C2, . . . , Cm, between which a respective sensor element RME isconnected. Each of the row or column conductors has an associated returnconductor which is used to return the respective conductor to anevaluation circuit (not shown).

[0021] This circuit arrangement allows sensor elements RME still to beinterrogated even when an interconnect is severed. In FIG. 1, the rowconductor R1 is broken. In this case, the break is between the points ofcontact between the row conductor R1 and the column conductors C2 andCm. In a conventional circuit arrangement, the result of such a break inan interconnect is that the sensor elements R1C1 and R1C2 can no longerbe interrogated. In the embodiment shown, this is not the case, sincethe two sensor elements in question can be interrogated via the returnline 10 associated with the row conductor R1.

[0022] One particularly advantageous embodiment of the invention isshown in FIG. 2. This figure shows a circuit arrangement in which,additionally, monitoring resistors RU are respectively connected betweenthe column conductors C1, C2, . . . , Cm and an additional row conductorR0 and between the row conductors R1, R2, . . . , Rn and an additionalcolumn conductor C0.

[0023] This embodiment allows both a returned column or row conductorand the associated return conductor to be checked by checking therespective resistance for the additional row or column conductor. Thisallows clear establishment of whether and, if appropriate, in whichconductor a line break has occurred.

1. A circuit arrangement comprising i sensor elements, said i sensorelements being interconnected in an (n×m) matrix circuit configurationwith n row conductors and m column conductors, where i, n and m arenatural numbers different than zero and where 1≦i≦n*m, wherein a firstconductor end of the n row conductors and m column conductors can beconnected to an evaluation circuit and where each of the i sensorelements is connected between two respective conductors from the rowconductors and column conductors, characterized by at least one returnconductor whose first conductor end can be connected to the evaluationcircuit and whose second conductor end is in contact with the secondconductor end of one of the row or column conductors.
 2. The circuitarrangement as claimed in claim 1, characterized in that the firstconductor end of the return conductor and the first conductor end of thecontacted row or column conductor can be actuated in parallel by theevaluation circuit.
 3. The circuit arrangement as claimed in claim 1 or2, characterized in that the first conductor end of the return conductorand the first conductor end of the contacted row or column conductor canbe actuated separately by the evaluation circuit.
 4. The circuitarrangement as claimed in one of claims 1 to 3, characterized by anadditional row conductor, with the second conductor end of at least onecolumn conductor being in contact with the additional row conductor. 5.The circuit arrangement as claimed in claim 4, characterized in that thecontact is made by means of a resistor element.
 6. The circuitarrangement as claimed in one of claims 4 or 5, characterized by areturn conductor whose first conductor end can be connected to theevaluation circuit and whose second conductor end is in contact with thesecond conductor end of the additional row conductor.
 7. The circuitarrangement as claimed in one of claims 1 to 6, characterized by anadditional column conductor, with the second conductor end of at leastone row conductor being in contact with the additional column conductor.8. The circuit arrangement as claimed in claim 7, characterized in thatthe contact is made by means of a resistor element.
 9. The circuitarrangement as claimed in one of claims 7 or 8, characterized by areturn conductor whose first conductor end can be connected to theevaluation circuit and whose second conductor end is in contact with thesecond conductor end of the additional column conductor.